There is a need for an inexpensive, effective, yet safe and convenient method to minimize the microbial burden of objects we interact with. In addition, this method must not leave behind microbes with resistance to future treatment. This need is primarily evidenced by unacceptably high rates of infection in hospitals and health care facilities. But there are also problems in daycare facilities, schools, the food industry and the travel industry, among others. Additionally, these problems are becoming more severe as microbes which are resistant to virtually all known antibiotics are becoming more common. It has been predicted that we may soon enter a post-antibiotic era that will be similar to the pre-antibiotic era in which even minor infections will be life threatening.
Consequently, a method for killing virtually all microbes is needed that prevents the microbes from developing a resistance and with ingredient compounds that are not hazardous to humans, pets and other beneficial life that may be exposed to them. A potential way to do this would be to utilize ingredients and methods that are relatively safe to humans but are biocidal.
For centuries prior to the antibiotic era, humans had safely utilized natural biocides. Vinegar has been well known to protect foodstuffs from the effect of microbes, evidenced by many foods being pickled. Ethanol (drinking alcohol) has also been used for years. In Europe, for example, medieval monks who brewed and drank wine or beer instead of the local water had much longer life spans. Additionally, certain spices, essential oils, and honey also have antimicrobial properties. More recently, hydrogen peroxide has been shown to fight microbes, and has long been an internal method that evolved in the animals' eternal fight against the microbes that infest them. Electricity has a biocidal effect. Also, sunlight emits energy in the ultraviolet wavelengths, what is well-known for its biocidal properties.
The problem with these safe biocides is that each one individually is not effective against all types of microbes, and several target microbes have developed defense mechanisms against these biocides. However, combinations of two or more of these biocides have proven to work synergistically to enhance each one's effects. Particularly, combining hydrogen peroxide and acetic acid (the primary component of vinegar) to form peroxyacetic acid has proven to be especially effective. Several methods, apparatuses, and disinfecting systems utilizing peracids, including peroxyacetic acid, have been described in U.S. Pat. Nos. 6,692,694, 7,351,684, 7,473,675, 7,534,756, 8,110,538, 8,696,986, 8,716,339, 8,987,331, 9,044,403, 9,050,384, 9,192,909, 9,241,483, and U.S. Patent Publications 2015/0297770 and 2014/0178249, the disclosures of which are incorporated by reference in their entireties.
However, one of the biggest drawbacks with using peracids is that they are easily hydrolyzed to produce ordinary acids and either oxygen or water. Consequently, peroxyacetic acid has limited storage stability and a short shelf life. Peroxyacetic acid instability is described in detail in U.S. Pat. No. 8,034,759, the disclosure of which is incorporated by reference in its entirety. Often, commercially available products contain additional components to combat this problem, by including either a large excess of hydrogen peroxide to drive equilibrium toward the peracid form, or stabilizers such as other acids, oxidizing agents, and surfactants. Some methods have prevented degradation during shipping and storage by requiring that individual components of a peracid composition be mixed together, and subsequently applied, at the location and time that a target will be disinfected or sterilized. Yet these methods nonetheless require expensive additives that are difficult to obtain, such as polyhydric alcohols, esters, and transition metals, as well as specific reaction conditions.
As a non-limiting example of the measures taken to stabilize peracid compositions, U.S. Pat. No. 8,716,339 describes a disinfectant system that includes a first chamber containing a first solution that includes an alcohol, an organic carboxylic acid, and a transition metal or metal alloy, and a second chamber containing a second solution that includes hydrogen peroxide. Prior to disinfecting, the system is configured to mix the first and second solutions prior to dispensing the mixture onto a surface. Mixing the first and second solutions forms a peracid within the disinfectant system prior to dispensing, but the presence of the transition metal is required to help stabilize the peracid in the period between when the solutions are mixed and when the mixture reaches the contaminated surface.
Similarly, U.S. Pat. No. 8,110,538 describes microbicidal, antimicrobial, and decontaminant compositions containing peroxides and peracids with equilibrium reaction products in combination with photoreactive surfactants and polymers, wherein the polymer interacts with the peracids and peroxides. Such equilibrium reaction products include organic acids such as acetic acid and other carboxylic acids. By including an excess amount of hydrogen peroxide and an organic acid, the composition leverages Le Chatelier's principle to drive equilibrium away from peracid hydrolysis, stabilizing the presence of the peracid within the composition. Furthermore, the polymer further acts as a stabilizer by forming adducts and chemical complexes with the peracids and peroxides within the composition.
In both of the above examples, the additionally-added components serve to stabilize the peracid compositions prior to dispensing them onto a surface to be disinfected. However, these components are expensive, relatively scarce, and can have undesirable effects within the environment to be disinfected. Such undesirable effects often include the leaving of residues, films, stains, and pungent odors on treated surfaces and surface areas that require time, money, and effort to remove, if they can be removed at all. Even if those undesirable effects can be later remedied, there are known safety concerns associated with dispersing airborne particles or peracids into the environment in an effort to sterilize that environment. Safety data and recommended exposure levels are described in detail in Acute Exposure Guideline Levels for Selected Airborne Chemicals, National Research Council (US) Committee on Acute Exposure Guideline Levels, pg. 327-367, Volume 8, 2010, the disclosure of which is hereby incorporated by reference in its entirety.
As a result, there is still a need for sterilization and disinfecting methods utilizing peracids that are simultaneously effective, convenient, and safe, while at the same time using cheap and readily available materials.